Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: M. Riccardi x
  • All content x
Clear All Modify Search

Abstract  

An archaeometric investigation on plaster samples taken from the cellars of the Visconti Castle in Pavia has brought out the existence of several layers and colour films of various periods. The oldest plaster spread over the masonry is formed with three main layers. Above them, one film of bluish-black colour can be found on the arcs and on the bearing walls. On this black layer, a white film of calcitic composition, containing also apatite fragments, was spread. These ancient materials were subsequently covered in more recent times with plasters having different compositions and textures. In the present paper the properties of the three main plaster layers and those of the black film are reported in detail. The thermal behaviour of these materials was studied by means of differential thermal analysis and thermogravimetric analysis. The study was completed with scanning electron microscopy,microprobe analysis and X-ray diffraction on powders. The results obtained provide interesting clues for advancing reasonable hypotheses both on the methods adopted in ancient building yards, and on the techniques for the production of the pigments employed.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: C. Tomasi, M. Scavini, A. Speghini, M. Bettinelli, and M. Riccardi

Abstract  

The devitrification of glassy PbGeO3 was studied and interpreted by means of isothermal and non-isothermal Johnson-Mehl-Avrami equations. In the case of the non-isothermal approach, several approximated equations proposed by various authors were considered in order to obtain both the activation energy E a and the Avrami morphological coefficient n of the crystallisation process. A critical discussion of the Avrami coefficient on the basis of experimental morphological evidence is also presented.

Restricted access

Abstract  

The reproducibility, the small scale as well as the large scale variability of137Cs extracted sequentially from the soil by using a modified Tessier procedure was investigated at several grassland sites in Bavaria/Germany and in the Chemobyl area. Because undisturbed grassland soils are never homogeneous with respect to their soil properties, all sequential extractions at the German sites were carried out at each plot separately for different soil layers (e.g., 0–2, 2–5, 5–10, 10–15, 15–20 and 20–30 cm). The results show that the coefficients of variation (CV) for the reproducibility of the extraction procedure for137Cs was (with some exceptions) around 10–20% for all fractions. For the small scale variability of137Cs (samples within an area of 10×10m2) the values for theCV were (again with a few exceptions) in the same range. Compared to that, the large scale variability of extractable137Cs (random soil samples within an area of 100×200 km2) was higher for all fractions, even though only moderately. The implications of these results with respect to a sampling design are discussed.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: A. Marini, V. Berbenni, G. Bruni, R. Riccardi, and M. Villa

Abstract  

The thermodynamics of β-cyclodextrin dehydration is investigated, by parallel DSC/TG experiments, on both fully and partially hydrated samples. The apparent dehydration enthalpies per mole of water are impossibly high and this fact suggests that another phenomenon, in addition to the rupture of the β-cyclodextrin/H2O hydrogen bonds, contributes to the peak area. All the experimental evidence agrees with an ‘interaction model’ which assumes that deydration is accompanied by a slow and reversible rearrangement of the β-cyclodextrin structure.

Restricted access

Abstract  

The kinetics of a poly(methyl methacrylate) (PMMA)-modified epoxy resin cured with different functionalities amine mixtures was analyzed using differential scanning calorimetry (DSC) in both isothermal and dynamic conditions. A delay in the reaction rate was observed which increased with PMMA content. An approach of kinetic features involved in curing was carried out. A linear dependence of preexponential factors of neat systems with modifier content was considered. The approach shows the contribution of other factors including the dilution effect of the functional groups to the observed delay. Fourier transform infrared spectroscopy (FTIR) indicated a noticeable change in the interactions present in neat systems due to the presence of PMMA. On the other hand, a significant influence of the ratio between each amine in the epoxy/amine mixtures on the final physical appearance was observed. At constant curing conditions, materials from completely opaque (phase separated) to transparent (miscible) were obtained with the increase in monoamine content.

Restricted access